1. Field of the Invention
The present invention relates to a method and system for measuring dimensions of a shape of a circuit pattern, which is formed on a wafer, using an electron microscopic image of the circuit pattern in a process of manufacturing a semiconductor device.
2. Description of Related Art
Dimensions and shape of a multi-layered pattern formed on a wafer as a substrate are important factors having a great influence on performance of the semiconductor device in a manufacturing process of a semiconductor device. In particular, a wiring pattern including a transistor gate wiring has a strong connection with its wiring width and shape, and accordingly, it is very important to build a manufacturing process to realize a desired wiring shape.
A general pattern of a semiconductor device is produced using an exposure technique. A fine pattern is formed by forming a film such as a photosensitive organic material (also called a photoresist) on a target material, exposing and developing a desired pattern, and etching the target material using the formed photoresist pattern as a mask.
In production lines of semiconductor devices, dimensions of the photoresist pattern after the exposure and development or dimensions of the pattern after the etching are commonly measured and controlled using a CD-SEM or the like. Scanning electron microscopes for line width measurement (for example, CD-SEMs (Critical dimension Scanning Electron Microscopes)), which are capable of picking up an image of a wiring with hundred thousand magnifications or above, have been conventionally used as length-measuring tools for measuring a fine wiring width of about several tens nanometers. As disclosed in ┌International Technology Roadmap for Semiconductors 2005 Edition, Metrology (Http://www.itrs.net/)┘, measurement by CD-SEMs requires high repeatability and reliability. For measurement with high precision using an electron microscopic image (hereinafter referred to as an SEM image), it is effective to use an image with high contrast, low noise and good quality.
In the mean time, among materials commonly used in recent semiconductor manufacturing processes, there are many materials having low electron beam radiation-resistance, such as ArF resists or Low-k materials, as disclosed in ┌A. Habermas, D. Hong, M. Ross, W. Livesay, “193 nm CD Shrinkage under SEM: Modeling the Mechanism” Proc. SPIE 4689, pp. 92-101 (2002): (Habermas et al.)┘. When a pattern made of such materials having the low electron beam radiation-resistance is measured, it is preferable to limit the amount of radiation of electron beams to be as low as possible in order to reduce damage to the pattern. In general, in measurement for a sample having low electron beam radiation-resistance, it is difficult to use a high quality image having a high S/N ratio. For this reason, such a sample has to be subjected to an image smoothing treatment or the like to reduce an effect of noise, thereby improving repeatability of measurement.
In addition, a method of measuring dimensions of a pattern in consideration of a sectional shape of the pattern with attention paid to a relationship between the pattern shape and a waveform is disclosed in ┌J. S. Villarrubia, A. E. Vladar, J. R. Lowney, and M. T. Postek, “Scanning electron microscope analog of scatterometry,” Proc. SPIE 4689, pp. 304-312 (2002): (Villarrubia et al. −1)┘. Specifically, this disclosed method is to measure a pattern sectional shape and dimensions of the pattern with high precision based on the pattern sectional shape by calculating a relationship between the pattern sectional shape and a waveform of an SEM signal through a Monte Carlo simulation, storing the calculated relationship as a library, and selecting waveform data nearest to an actual SEM image for measurement of dimensions of the pattern.
Furthermore, an example of obtaining a CD value of bottom, top, signal peak interval and the like of an SEM image signal as an example of sites selected as image features when the image features varying depending on a pattern shape are calculated from an obtained waveform is disclosed in ┌Chie Shishido, Ryo Nakagaki, Maki Tanaka, Yuji Takagi, Hidetoshi Morokuma, Osamu Komuro, and Hiroyoshi Mori, “Dose and focus estimation using top-down SEM images,” Proc. SPIE 5038, pp. 1071-1079 (2003): (Shishido et al)┘.